In order that a sample technique may produce dependable, and reliable results, a sample should have the following essential characteristics :
- Representativeness: The sample selected should truly represent the characteristics of the universe. For this, the investigator should be free from all bias, and the method of selection should be appropriate.
- Adequacy: The size of the sample should be adequate i.e. neither too large nor too small but commensurate with the size of the population.
- Homogeneity: There should be a homogeneity in the nature of all the units selected for the sample. If the units of the sample are of heterogeneous character it will be impossible to make a comparative study with them.
- Independentability: The method of selection of the sample should be such that all the items of the sample are selected in an independent manner. This means that selection of one item should not influence the selection of another item in any manner, and that each item should be selected on the basis of its own merit.